Television pick-up tubes



March 19, 1957 R. THEILE TELEVISION PICK-UP TUBES Filed May 5, 1952Inventor Rachcu-d Thefle.

2m w iierw m4! Attorney 2,786,157 TELEVISION PICK-UP TUBES RichardTheile, Cambridge, England, assignor to Pye Limited, Cambridge, England,a British company Application May 5, 1952, Serial No. 286,069 7 Claimspriority, application Great Britain May 9, 1951 Claims. (Cl. 315-11) Thepresent invention relates to television pick-up tubes of the storagetype in which the scanning of the storage surface or target is effectedby high-velocity electrons, for example of the order of 1000 volts.Tubes of this type include those known as iconoscopes andimage-iconoscopes.

Various proposals have previously been made to incorporatesecondary-electron multipliers withinthe pickup tube for improving itssensitivity. Hitherto, however, satisfactory results from the use ofsecondary-electron multipliers in pick-up tubes with high-velocityscanning have not been commercially achieved, and secondaryelectronmultiplication is only incorporated in pick-up tubes with low-velocityelectron scanning (for example image-orthicon tubes), as in such tubesthe signal current from all parts of the storage plate returnssubstantially to the electron gun where it can be easily collected anddirected into the multiplier.

The diiiiculty in obtaining satisfactory secondary-electronmultiplication in high-velocity-scanned tubes is caused by the fact thatthe signal current consists of low-velocity secondary electrons whichare released with different initial velocities and different directionsof emission at different parts of the storage plate and are collected bythe collector electrode,'usually in the form of a conducting wallcoating inside the tube envelope and surrounding the storage plate.

The present invention has for its object to provide an arrangement whichreduces or overcomes the difficulties in collecting and accelerating thesignal electrons from all parts of the storage plate of ahigh-velocity-scanned tube, and thereby enabling efiicientsecondary-electron multiplication to be obtained. For achieving theresults according to the invention two problems have to be solved,namely (1) collection of the secondary electrons into the multipliermust be substantially uniform over the whole surface of the storageplate, and (2) thepotential at which the surface of the storage platestabilises must only be effected to a small extent by the potential ofthe first multiplier electrode (dynode) since it is essential tomaintain a suflicient potential difierence (of the order of 100 volts ormore) between the surface of the storage plate and the first dynode inorder to obtain the necessary acceleration of the collected secondaryelectrons for producing a high secondary-emission ratio in themultiplier system. 7

According to the present invention, the multiplier is constructed in oneor more sections extending around the front of the storageplate surface,the multiplier electrodes being screened from the storage plate by ascreen or screens maintained at a potential which is substantially less(of the order of a hundred volts or more) than the potential of thefirst multiplier dynode, and preferably at a potential which isapproximately the same as the potential of the internal wall coating ofthe tube, the screening action of a screen being such as to reduce thepenetration of the positive field of the associated first multiplierdynode to such a small value that the storage surface stabilises at apotential which is positive with respect, to the wall coating or otheradjacent electrodes but is low with respect to the potential of saidfirst dynode, whilst permitting a sufficiently high field penetration toeffect collection of substantially all the secondary electrons releasedfrom the storage surface by the multiplier. As the mean velocity of thereleased secondary electrons is generally of the order of 2 to 3 voltsand the optimum dynode potential is approximately '100 or more volts, afield penetration of less than 10%, for example about 3%, provides asuitable compromise, that is to say, that in the triode systemconsisting of the storage plate, the screen and the dynode, about 3% ofthe positive field of the dynode should be present at the surface of thestorage plate.

In a preferred embodiment, in which an electron multiplier is utilisedin conjunction with an image-converter tube, for example an imageiconoscope, the photo-cathode of the tube is arranged to be operativeonly during the picture-blanking intervals (frame-blanking intervals andline-blanking intervals) when the tube is operating under high levellight conditions, so that the photo-current is source 22.

constituting the collector electrode of the tube.

interrupted during the actual scanning of the tube. This enables thenoise level to be reduced under such highlevel light conditions.

In order that the invention may be more fully understood, reference willnow be made to the accompanying drawing, in which: I

Fig. 1 shows a pick-up tube of the image-iconoscope type constructedaccording to the invention,

Fig. 2 shows a detail view of a modification.

The pick-up tube shown in Fig. l is of the imageiconoscope type, andcomprises an evacuated envelope 1 formed in known manner at one end witha photocathode 2 on which the picture to be projected is focussed by alens 3. The released photo-electrons are focussed by the focus coil 4onto the storage plate 5 backed by the signal plate 6, the focus coil 4being energised from a suitable potential source 19. The storage plateis arranged to be scanned by an electron gun 7 fed from source 20 andlocated in a side tube of the envelope 1,

the scanning beam being focussed and deflected by the focus coil 8energised from potential source 21 and defleeting coils 9 fed withmodulating waveforms from The internal surface of the envelope-1 isprovided with a conductive Wall coating 10 normally The tubeconstruction as so far described is conventional and V well-known in theart.

According to the present invention, the tube also includes an electronmultiplier which may be in the form of a ring structure generallyindicated at 11, the axis be co-axially mounted .if desired. Themultiplier electrodes constituted by the first, second, third and fourthdynodes 12, 13, 14 and 15 respectively and the collector 16 are enclosedin a screening box 17, the end of which facing the storage plate 5 iscovered by a screening mesh 18 through which the secondary electronsreleased from the storage plate 5 pass to impinge upon the first dynode12. The screening box 17 and mesh 18 may be held at approximately thesame potential as the wall coating 10 and are held at a potentialsubstantially less (of the order of a hundred volts or more) than thepotential of the first dynode 12, as shown schematically by theinterposition of potential source 23. The size of theapertiire in thescreening mesh 18 and its spacing from the first dynode12 are sodetermined that there is about 3% penetration of the positivefield ofthe first dynode into the space near the storage plate. Such a lowfieldv [the noise' level in the'picture is producedlbylthe-shotcflenetrationsdoesnot substantially imreaseaie potential nly"duiing"thepictur blanking "intervals which' may i at which .thetsturface. .of thestorage. plate tstabilises, t whilst s :betihetframe.blankinginterzvalsand/or.thetlineablankit is sufiicient to accelerate.and cause the secondary elecing intervals when the tube is operatingunder hightrons to be collected by the multiplier. The field penelightconditions so that the photo-current is interrupted z:.t'ration should,furthermore, be such that the' potential during the actual scanning ofthe tube. at-which the surface of. the storage'plate stabilises is Tobring this about, the photo-cathode 2 may be biassed positivewithrespecttoi-the wall"coatingxso'thatthe latter negatively by a series'lofipblses corresponding to the -produces azretarding fieldto the-secondary electronsand picture-blanking-pulses. In the embodimentillustrated, --the latterare not'lost tothesurrounding electrodesbut thebiassing'p'ulses are'produced by'a pulsing device 30 r; ar llt d b th 1t1i -although;-if'desired;'theyrmay be obtained by appropriate wAccording t l featurezofjthejnventioh, the ratio ofvolt'age'amplificatiom of theblan'king pulses. 'A switch 31 :thediameter of the annular multiplier 'structurerto Y the may beincorporated to cut out the biassing pulses and distance between thes-creening mesh' and-the-storage to bias'the photo-cathode 2continuously for continuous plateis made such as to'producea"substantially'uriiform photo-emissiontwhenxthei tube: .isoperatingunderllowfieldover the' surface-of the storagefplate Since" thelight conditions. Thepulsing device..30 is connected to a insulatingsurface of the storage plate st abilises approxisuitable source32"for'tl1e production of the negative pulses. mately to the' adjacentspace potential, anyno'n-uni- If desired, m ans may he pr d d f rperating the .wf it i h Space t i l p d d-b th fi ld f switch 31automatically in dependence upon the amount the multiplier dynode wouldcause different portions of l f available light'in'the'scene or pi betransmitted- -'the= storage plate to stabilise 'at "differentpotentials,W a-p t m im n h s beefldescribed; it therebygiving rise to spurioussignals. The-ratio ofthe vv'llillhbe understood r Various modificationsay be --said' diameter and distance isso chosen that th'estorage BW h pfi Scope bf the inventionhplate is. a i i where th fi ld i fi Thus," forexample,th'e screenassociated with the first fiatness; the influenceexerted by the signal plate and dY e h e in the f of a mesh as Shown at18 the wall coating on this field being-takenint-o account. 7 25511 i yb eollstrueted from sheevmaterial -The distance between the first dynodeand the screenh one more apertures r slbtsftbereirh Sheba modi- 1 ingmesh, as well as the relativepotentials therebetween, fieatibllfl us r db zf h' Shows y a "have an -effect upon this field. Further,*by varyingthe Pa of h fp t f screening'box 17a having relative potentials of thescreening-box and the wall'c oati r u formed of sheetmarerial.Providedwith all inggfor example by making the potentialtofithe former"ranr1ular SlOt'18a 'faClng" thestorage plate. 5. The firstcs'lightlypoisitive or negative with respect to the potential dy 5arranged Within the Screening box dof the latter, shown schematically byinterposition of the e hr 'eleetr 0118' released therefrom r collected.y source 24,which'n'1akes the potential of the screening l e t 6 r b rWlthlll' the from Seetioh of box slightly positive with respect to thecoating 10, slight n e h r e aperture: 13a r y correction may" beeffected in thefield disposition in Fheflange p' soifllat the collector16a has 110 order to obtain field uniformity'over thesurfaceof the uen rthe cblleetlohl ofz'the secondary electrons Storage plam leasedfrornthe'surface of thestorage plate.

' lf'desired, the geometry of the arrangement or? theFurthermore;theiimumplier structure'beed not be in potentials applied todiiferent parts thereof may be adthefiormiof clrculal' rmg but can be ofy other e011- justed. to producev a desired non-uniform fiel'd over theirem tish p br examplef rectangular form r plate, to compensate for orOther ;spond1ng'approxrrnately'to the'shape of the picture on theSpurious signals. storage plate. The'mult1pl 1er7may'be constructed as aAccording to a further feature of the invention, the smgle un t fromPlurahty 0f vseParate seetlehe Which surface of the storage plate 5 isconstructedlto possess Y be p q pa'rt; for example it may c m t fDur asmall "amount of surface leakage in order to equalise sk f l h us emb dt form a rectangular m any residual unevenness of the surface potentialof. the iphernstl'ucturei the ends" bf'the Sections Preferably beingstorage plate without noticeable dilution of the charge close q patterndue to the picture storage. =may "be i' i 1 v [achieved by providing'thesurfacev 'of lilldsforag q l 1; 'Intelevision"transmittingapp'aratus,.tl1e combination "with a slightly con-ducting layerf 25,which may,.,for. .in- 9 .P '1 P tube of Zrhe ehargeesltorage yp i astance be made of glass. An insulating layer'26isinterclfargefstoragermrget with means for Scanning Said-target posedbetween the conducting layer 25. and lthe surface 'Wlth 'abeam ofhigh'velocity s a ma 5 peripheral regions of storag surfa c gmay tlOD.device located between saidtarget andsaid be formed with conductingelectrodes. 27 which; if he Scanning means and-Out Of-the p the ing asired, .may' be connected to a. source ZSJofbiastfoi-biasf QmPr at leastdY a Collector l singthe"surface of the storage plate. "Preferably; thetrode arranged in-an enclosed hollow structure surround- "source 28 isadjustable under control of controlimeming the scanning bearnpanelectron-permeable:electrode 29 between said-multiplier device and'saidtarget, and? means "With a pick-up .tube such as sofarfdescribed' above,for: applying potentials to said multiplier device and to said'electron-permeable electrode for producing; a fieldpenetration ratioofthe adjacent dynode of said' multiplier .-.device through 'said electronp'ermeable.electrode to said charge-storage target which is less th an'10%.

'2. A television pick-upi tube of thestorage type in which :the;scanning of the charge-storage target is eifected by V v V v V".high-velocity-electrons,comprising .a-secon'dary-electron "Ith g Homey a p Hewevertr-under "multiplierlocated between's'aid target and thesome of 'h h l- S the 161181 adjustment (aperturey fscanningelectronsfsaid'rnultiplierdevice comprising at ethepick-upttu'be isrmore criticaliin ordento; avoid'noise, ideast one dynode and acollector electrodeto'ta'lly'enclosed Les theincreased-ljight,whichirnproves therpicturepcauses "within an enclosed hollow structurefacing said'targetj the -.excessive.;noise. face of said structureconfronting said 'charge storage -"-Another featureof;:the::inventionzzhasicforzfitss object -target co'rnprisin'g a" meshelectrode. l-toovercome orgreduceltthisfiifficulty andx'to' this end the1 39A" 'tele'vision pick-up tube of the storage type in mbedsarran-gedto hav-itszphoto+cathdde lzfioperative which the scanning of thecharge-storage target serrated noise of the scanning beam current andalso of the=photocurrent' itself. When operating under low-light.conditions for which the mu-ltiplier tnbe is mostsuitablquthe averagephoto-current is' less. than oratihlrhbstqual 6 to,"the scanning-beamcurrent, so .that thennoisefldueflto thefphoto-current is not;appreciable and ionlyglincreases smugplier consisting of at least onedynode and a collector electrode totally enclosed vithin an annularenclosed hollow structure facing and closely adjacent said target, thewall of said structure confronting said charge-storage surfacecomprising an annular mesh electrode. I

4. A television pick-up tube comprising an envelope, a charge-storagesurface within said envelope at one end thereof, a tubular memberprojecting from said envelope at an acute angle and communicating withthe interior of said envelope and pointing towards said charge-storagesurface, a source of electrons in said tubular member for producing abeam of electrons for scanning said chargestorage surface, and anelectron multiplier consisting of at least one dynode and a collectorelectrode enclosed within an annular enclosed hollow structure facingsaid target and whose axis is off-set with respect to the longitudinalaxis of the envelope and located out of the path of said beam ofscanning electrons, the wall of said enclosed hollow structureconfronting said target comprising an annular mesh electrode.

5. Apparatus for transmitting television signals, comprising atelevision pick-up tube comprising an envelope, 2. charge-storagesurface within said envelope at one end thereof, a tubular memberprojecting from said envelope at an acute angle and communicating withthe interior of said envelope and pointing towards said charge-storagesurface, a source of electrons in said tubular member for producing abeam of electrons for scanning said chargestorage surface, an electronmultiplier consisting of at least one dynode and a collector electrodeenclosed within an annular enclosed hollow structure facing said targetand whose axis is off-set with respect to the longitudinal axis of theenvelope and located out of the path of said beam of scanning electrons,the wall of said enclosed hollow structure confronting said targetcomprising an annular mesh electrode, \a photo-cathode in said envelopeat the end thereof opposite said charge-storage surface, and means forblanking out said photo-cathode during the time that the scanning beamis scanning said chargestorage surface.

References Cited in the file of this patent UNITED STATES PATENTS2,230,134 Colberg et a1. Jan. 28, 1941 2,237,896 Vance Apr. 8, 19412,374,914 Behne et al. May l, 1945 2,611,820 Somers Sept. 23, 19522,652,515 McGee Sept. 15, 1953 FOREIGN PATENTS 635,712 Great BritainApr. 12, 1950

